The RPK kits Inter/ord has been trying to dump for the last seven years had barrels so entirely shot out, you could drop a 7.62 bullet down the muzzle and it would rattle around with room to spare on the way down...I've never seen another consistant group of kits or guns with so much wear...It seems that was a popular way to determine barrel condition and has caught on. It is over used with most guns in reasonable condition as it tells you absolutely nothing other than it's not a shot out sewer pipe...